The proposed neuroanatomical and electrophysiological studies continue investigations of the organization of pathways that mediate vestibular influences on autonomic and limbic pathways, particularly in pathways that mediate the linkage between balance disorders and anxiety disorders. Three circuitry networks appear to be critical for balance-anxiety link: a vestibulo-parabrachial nucleus (PBN) network, coeruleo-vestibular (noraderenergic) network and raphe-vestibular (serotonergic and non-serotonergic) networks. The physiology and connections of the PBN network will be studied in primates; the organization of the noradrenergic and raphe pathways will be explored in rats. Our on-going primate studies have shown that a caudal region of PBN contains neurons that receive vestibular nuclear input and are sensitive to whole body rotation. New electrophysiologic studies in alert primates are directed at elucidating the spatial organization of responses of parabrachial nucleus neurons during whole body rotation. Two main foci will be characterization of otolith-related responses and a test of the hypothesis that responses will differ for predictable and unpredictable whole body rotation in three dimensions. Anatomical studies in primates are also designed elucidate the afferent and efferent connections of this vestibulo-recipient region of PBN. Our on-going studies have shown that the dorsal raphe nucleus, nucleus raphe obscurus and nucleus raphe pallidus provide serotonergic input to the vestibular nuclei. Anatomical studies will elucidate the topography of these projections, the distribution of immunoreactive serotonin receptors in the vestibular nuclei and test specific hypotheses regarding the organization of collateralized raphe projections to the vestibular nuclei and other sites. Finally, anatomical studies in rats will test specific hypotheses regarding the organization of collateralized noradrenergic projections to the vestibular nuclei and other sites.